Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny with isolated showers. Highs around 86 near the shore to around 74 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 68 to 73 near the shore to around 59 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to around 73 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs around 82. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 73 to 80 in the valleys to around 64 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 64 in the valleys to around 54 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday: Mostly cloudy with numerous showers. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 76 to 85. East winds 10 to 15 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 72. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 75 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 73. East winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 83. East winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will continue through the weekend, with clouds and showers favoring windward and mauka areas. An upper low will linger near the state and could enhance showers over windward areas Sunday night into Monday. After decreasing late Sunday through Tuesday night, stronger trades will return by midweek. Expect drier conditions from Tuesday onward.

Discussion

High pressure persists far northeast of the main Hawaiian Islands, driving moderate to breezy trade winds across local waters this morning. Satellite loop shows scattered to patchy broken low clouds across most windward slopes of the smaller islands. Overcast low clouds dominate windward and Kau shores and slopes of the Big Island. An area of overcast low clouds across waters lee of Oahu and the islands of Maui County appear to be moving away within trade flow. Radar shows isolated to scattered showers within cloud cover, with the bulk of shower activity noted within the cloud cover just lee of the central islands. Models show the high will remain nearly stationary for the next several days which means that moderate to locally breezy trade winds will continue across the island chain through the weekend, with only slight diurnal speed variations. Trade winds will decrease late Sunday through Tuesday night due to a brief weakening of the ridge north of the state.
Expect mostly light showers embedded within the trade wind flow today that will favor windward and mauka areas. An upper low about 200 miles north of the islands may deepen and shift slightly south and west by Sunday, possibly enhancing trade wind showers. Models show trade flow will advect increased moisture across the islands within the next day or two. This moisture, combined with instability associated with the upper low, may trigger brief heavy trade showers Sunday night through Monday. This could result in pockets of heavier than normal rainfall for windward areas. Models show a steepening pressure gradient over the islands as the high far to the northeast drifts southwestward. This could result in trade winds increasing into the breezy to windy range by the middle of next week. Expect drier trade wind weather by Tuesday.

Aviation

The ridge to the north of the islands will continue to bring moderate to locally breezy trade winds to the region through the weekend. Satellite shows limited clouds over and immediately upstream of the islands. Additional clouds and showers are expected to be carried in on the trade wind flow, favoring over the windward and mauka areas.
An upper level low just north of the islands may help to enhance some of the showers. The overnight soundings at Lihue continues to show no trade wind inversion in response to the proximity to the upper level low. For the western end of the state, the lack of an inversion is limiting mechanical turbulence to the lee of the mountains.
Meanwhile the trade wind inversion remains strong over Hilo overnight, but has lifted to around 8000 feet. This will allow any showers moving over the eastern end of the state to grow a little taller than yesterday. Lighter winds over the leeward sides of these islands is allowing for some afternoon cloud development.
Surface winds over the eastern end of the state are strong enough to bring the possibility of low level turbulence to the lee of the mountains. However as the trade wind inversion lifts, its less likely that turbulence will be experienced. AIRMET Tango remains in effect for moderate low-level turbulence over and to the lee of Molokai Maui and the Big Island, however it may be dropped later today if the inversion height lifts further.

Marine

Fresh to strong easterly trades will continue through the weekend, then briefly ease into the moderate to fresh category Monday and Tuesday as a weakness in the ridge forms to the northwest. Easterly trades will surge back Wednesday through the second half of the week as the ridge strengthens. Trades could briefly dip below the Small Craft Advisory threshold over the windier waters between Molokai and the Big Island Monday through Tuesday.
Surf along exposed north and west facing shores will rise Sunday morning through early next week, with a peak centered on Monday, as a moderate (medium period), west-northwest swell arrives and moves through from former Typhoon Guchol. Recent satellite data confirmed this potential and showed a decent sized area of strong west-northwest winds aimed at the islands down the 305-315 degree directional band with seas in the 15-20 ft range around 1200 NM from the islands. SOFAR drifter buoys near the fetch region depicted the model guidance is on track or lines up well observations, which has this swell arriving and reaching the 2-3 ft range by late Sunday, then up to 4-5 ft Sunday night through Monday as it peaks. This will linger into Tuesday, then fade through midweek. There is a compact system trailing this feature east of Japan, which could keep the surf from going flat Wednesday through Thursday with a small swell holding out of the same west- northwest direction.
Surf along east facing shores will remain small/choppy and gradually ease early next week as the aforementioned ridge weakens briefly. An upward trend is expected Wednesday through the rest of next week as the local and upstream trades return to fresh levels.
Surf along south facing shores will remain small each day through next week with mainly background south-southwest to south- southeast swell energy moving through. Although high pressure is currently parked in our typical swell window southeast of New Zealand, a powerful gale- to storm-force low currently evolving far south of the Tuamotus and Tahiti will be enough to generate a long-period south-southeast (170 deg) swell for next weekend (24-26).

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov